Why are you complaining about issues with Windows Media Player after a Windows 10 update in this Forum?

This is not a Windows Media Player issues Forum or a Windows 10 issues Forum.

Perhaps you should try here
https://answers.microsoft.com/en-us?auth=1 and browse to find either Windows 10 or Windows Media Player to ask a question about. And at the link try spending some time to learn how to use the browse and filter areas so you can best find where or what to
ask a question about before you bother posting a question.

If you spend time to learn how to use it you may end up posting correctly like this post
Windows Media Playerwhich "Applies to Music, Movies & TV|Windows Media Player".

The posting looks relevant. It is not the problem of Windows Media Player exactly. it more looks like a problem with underlying Media Foundation components, I would say that fragmented MP4 media source does not time stamp samples accurately and they pass
decoding without proper time indication for playback. Looks like API bug indeed.

Exactly. I can confirm this with a simple IMFSourceReader code. Just read the file with source reader and i print out timestamps. It does not do it right and it "quits" before reaching the end of the file.

The same code is fine on Windows 8.1.

This happened recently, like about 15-20 days ago, when my machine downloaded the updates.

As of 12/9/2016, I see a new updated mp4srcsink.dll, but I still see problems when first loading this file in Windows Media Player. The display initially remains blank and timestamps increment randomly until they are way past the duration of the
file. After seeking once, the file plays back correctly. Also hangs MFCopy, never completing.